1. Field of the Invention
The present invention relates to a plunger rod for use in a syringe or cartridge barrel having a plunger and containing a parenteral solution therein, or in a syringe or cartridge which are empty and are to be filled with a parenteral solution by the user at the time of administration.
The present invention also i-elates to a plunger rod for use in a syringe or cartridge containing a parenteral solution therein intended to be dispensed from a power injector.
2. Reported Developments
Syringes are cartridges made of glass or polymeric materials for dispensing parenteral solutions or withdrawing biological fluids from a patient are well known in the prior art. They comprise a cylindrical barrel with a tapered end at one end to which a needle or luer connector can be attached, and an open end which is stoppered by a plunger of a resilient thermoplastic or elastomeric material. The plunger serves the function of a stopper, when the barrel is filled with a fluid, or as a slidable member to expel the fluid from the barrel or to withdraw a biological fluid from a patient or another source.
In order to expel fluid from the barrel or to withdraw fluid into the barrel, the plunger is moved toward the distal end or toward the proximal end of the barrel by a plunger rod which is attachable to the plunger typically by screw threads. The user exerts a force, manually or by the use of a power injector, on the plunger rod to push and pull the plunger in the barrel. While the plunger rod does not contact the fluid in the barrel, it provides a very important function: it causes the plunger to move in an axial direction back and forth in the barrel when an external force is applied thereon.
The force applied to the plunger by the plunger rod should be perpendicular to the plunger so that the force exerted on the wall of the barrel by the plunger is uniform around the 360.degree. of its cylindrical configuration. To wit, the direction of movement of the plunger rod should always be perpendicular to the surface of the plunger. When the plunger rod flexes in the barrel, the direction of force on the plunger will not be uniform resulting in pressure points at certain areas of contact between the plunger and the inside wall of the barrel and, conversely, inadequate pressure points at other parts of the interface between the plunger and the inside wall of the barrel. Such pressure differences tend to allow leakage and difficulty in moving the plunger at an even rate in the barrel.
Recognizing the importance of dimensional stability, the prior art has incorporated various stability enhancing means into plunger rods which include the following.
The assembly disclosed in U.S. Pat. No. 4,543,093 has a plunger rod the central portion of which is almost as large as the inside diameter of the syringe barrel so that is will assist in keeping the plunger rod assembly concentrically aligned within the syringe barrel.
WO93/09827 discloses a shank having a plurality of longitudinal and radially extending vanes. In one preferred embodiment the shank is provided with four vanes in an "X" pattern while in another preferred embodiment the shank is provided with three vanes forming a "Y" pattern.
U.S. Pat. Nos. 5,700,247 and 5,860,961 disclose plunger rods having a plurality of vanes or support ribs.
A common feature of these plunger rods is a shank extending between the distal and proximal ends of the plunger rods having vanes or support ribs thereon. The vanes or support ribs are identical with one another running longitudinally on the shank and extending radially therefrom.
I have now discovered a strong, dimensionally stable plunger rod which is of novel configuration and is useful in combination with plungers intended for use in a syringe or cartridge barrel for manual or power injections.